Black is in trouble now.
27. h4h5  27... g6h7  28. c4b5 In two particular moments in this game, Carlsen plays extremely subtle moves that make it difficult for Black to defend. This is one of those educational moments. 28... c7c6  29. b5c4 The bishop simply goes back, but now the h2-b8 diagonal is open and the queen gains scope.